Photofilters and UV-absorbers have been employed for a number of years to protect coloring dyes from fading from exposure to light. UV-sunscreens have also been employed to protect skin from damage from exposure to sunlight. Representative references related to UV-sunscreens are:
U.S. Pat. No. 5,922,310 (Chaudhuri et al.) discloses a composition which includes a cationic antioxidant phenol in an amount of about 0.01-1% wt/wt.
U.S. Pat. No. 5,427,773 (Chaudhuri et al.); U.S. Pat. No. 5,427,774 (Chaudhuri et al.); and U.S. Pat. No. 5,451,394 (Chaudhuri et al.) discloses non-hydrolysable, non irritating, hair, skin and textile substantive quaternary salts of p-dialkylaminobenzamides.
U.S. Pat. No. 5,633,403 (Gallagher et al.) discloses substantive UV-absorbing cinnamido amine cationic quaternary salts.
U.S. Pat. No. 5,830,441 (Wang et al.) discloses a photostable UV absorbent with maximum absorption above 340 nm.
Recently, sunscreens also have been added to hair care products to guard against the deleterious effects of solar irradiation on the hair. Two sunscreens have been developed especially for hair, Escalol® HP 610 (U.S. Pat. No. 5,451,394) and Incroquat® UV-283 (U.S. Pat. No. 5,633,403). Unfortunately, they both suffer from inadequate photostability, meaning that they degrade in the presence of light, and they lack desired hair substantivity, meaning that they can not be effectively applied and retained on hair.
The ideal sunscreen formulation for hair or skin should be nontoxic and non-irritating to the skin tissue and be capable of convenient application in a uniform and continuous film. The product should be chemically and physically stable so as to provide an acceptable shelf life upon storage. It is particularly desirable that the preparation should retain its protective effect over a prolonged period after application. The product must be substantive to hair or skin so that it does not get washed-off quickly. Thus, the active agent when present on the hair or skin must be resistant to chemical and/or photodegradation and be substantive.
Techniques for stabilizing UV absorbent compositions are known. Representative disclosures in this area include U.S. Pat. Nos. 5,567,418, 5,538,716, 5,951,968 and 5,670,140.